This invention relates to a gradient index lens array assembly of the type used in short focal length optical systems for copiers and printers and, more particularly, to a relatively inexpensive lens array assembly comprising a plurality of lens arrays which are attached together lengthwise and whose output is optically coupled to project a single exposure line onto an imaging plane.
There are, at present, a number of commercial copiers which incorporate a gradient index lens array in an optical system to illuminate a document placed on a document platen. The lens array forms a focused, inverted erect image of the document on a charged surface of a photoconductor or imaging plane. The gradient index lens array comprises a plurality of light conducting fibers made of glass or synthetic resin which has a refractive index distribution in a cross section thereof that varies parabolically outward from a center portion thereof. Each fiber acts as a focusing lens to transmit part of an image of an object placed near one end, e.g., a document placed on a platen. An assembly of fibers, typically in a two row linear array, transmit and focus an image of the object. The fiber lenses are produced under the trade name "SELFOC"; the mark is registered in Japan and is owned by the Nippon Sheet Glass Co., Ltd. The lens arrays are characterized by having a short focal length and can be used in an optical system having a relatively short total conjugate, thus, enabling relatively compact copiers. Commercial copiers such as the Canon PC III. utilize lens arrays of this type. The linear array for this type of copier has a length equal to the length of the document being copied; e.g., a length of approximately 12 inches. The arrays are also used in copiers which reproduce large documents, such as blueprints and engineering drawings which may have widths up to 36 inches. The Xerox 2510 and 2520 copiers, for example, use a gradient index lens arrays having a 36-inch width. It is known that, as the length of the array increases, the manufacturing process becomes more complex and the yield decreases. This is one of the reasons that as lens arrays increase beyond 12 inches, the costs mount at a disproportionately higher rate. For example, to double a 12-inch array to 24 inches, would result in a cost increase greater than 5.times. rather than 2.times.. It is therefore desirable to provide a gradient index lens array capable of copying documents wider than the conventional 12-inch length while maintaining cost increases in proportion to the length increase. The present invention provides a lens array assembly which comprises two or more lens assemblies mounted in a staggered configuration to a common substrate. The ends of the lens array are masked along a common interface to enable an optical coupling of each lens array output. With this configuration, for example, three 12-inch lens arrays are physically mounted end to end and their outputs optically stitched together to effectively function as an integral or unitary 36-inch lens array forming a 36-inch line exposure at a photoreceptor. The combined cost of the three joined 12-inch lens arrays is a fraction of the cost of the single, unitary 36-inch lens array.
It is known in the art to electronically "stitch" together segments of imaging components in a optical system which includes a gradient index lens array. U.S. Pat. No. 5,260,718 issued Nov. 9, 1992 discloses linear print bars in a staggered two-row arrangement, the outputs of the print bars being electronically coupled and projected through a pair of tilted linear gradient index lens arrays to form a focused, exposed line on the surface of the photoreceptor. In U.S. Pat. No. 4,742,240 light is reflected from a pair of tilted arrays onto two rows of staggered CCD line sensors whose outputs are electrically combined. U.S. Pat. No. 4,147,928 discloses a similar concept where staggered sensors are imaged through an associated conventional lens. Not shown in the prior art is the concept of connecting a plurality of staggered gradient index lens arrays in the lengthwise direction and coupling the light outputs to form a single exposure line at a photoreceptor.
More particularly, the present invention relates to a gradient index lens array assembly comprising a plurality of linear gradient index lens arrays, each array having two staggered rows of optical fibers extending along the length of each array, each array connected in a staggered end-to-end configuration to form an extended length linear array assembly.